1. Field of the Invention
This invention relates to security paper and in particular concerns security paper made from nonwoven film-fibril sheets.
2. Description of the Prior Art
Security paper is used in the production of printed items that represent sufficient value to make them a temptation to forgery. In the past, security paper has been produced from high quality cellulosic papers. Usually these security papers include specific features or materials that are readily identifiable but very difficult to reproduce. The manufacture of many security papers involves spreading or distributing minor amounts of the identifiable materials in the paper pulp during the wet-consolidation of the pulp on a paper-making machine. Among the special identifying materials that have been included in security papers are fibrous material in various shapes, colored particles, silk threads, particles containing certain inorganic substances, fluorescent fibers, metallized fibers, metal wires, various non-fibrous thermoplastic materials and the like. Such identifying materials have been distributed throughout the security paper or have been contained in a layer near the mid-plane of the paper. Watermaking also has been used to provide special designs on the paper. Such security papers have found use in bank notes, paper currency, stock certificates, bonds, legal documents, passports, visas, travel tickets and the like.
French Pat. No. 1,347,240 discloses a process for preparing security paper. In this process nonwoven webs that contain bondable thermoplastic fibers are assembled with a discontinuous intercalary layer of identifying material and then bonded by means of heat and/or pressure. However, the patent does not disclose nonwoven sheets made of polyethylene film-fibrils nor how to prepare security paper therefrom.
Nonwoven sheets made from polyethylene film-fibrils are known, per se, from, for example, Steuber U.S. Pat. No. 3,169,899. Various methods of bonding such sheets are known, as, for example, from David U.S. Pat. No. 3,442,740. However, none of these patents concerning nonwoven sheets made from polyethylene film fibrils disclose the use of such sheets for security papers.
Applicant has now invented a process whereby a specific type of nonwoven polyethylene film-fibril sheet can be used to make a novel, strong, durable, high quality, security paper.